I've been searching google for ever, and I cannot find an example of how to do this. I also do not grasp the concept of how to construct a regular expression for SED, so I was hoping someone could explain this to me.

I'm running a bash script against a file full of lines of text that look like this: 2222,H,73.82,04,07,2012

and I need to make them all look like this: 2222,H,73.82,04072012

I need to remove the last two commas, which are the 16th and 19th characters in the line.
Can someone tell me how to do that? I was going to use colrm, which is blessedly simple, but i can't seem to get that installed in CYGWIN. Please and thank you!